Internet Control Message Protocol (ICMP)

One of the important parts we need to do while troubleshooting a network is to check the connectivity of two devices. We have many utilities to check the connectivity and availability of destination device. All these utilities are based on ICMP, defined in RFC 792. Internet Control Message Protocol (ICMP) is used to send error and control information between devices which support TCP/IP. Utilities like ping, tracert, pathping, etc work using ICMP. This tutorial explains the functions of Internet Control Message Protocol and the list of error messages generated by ICMP.

Important Functions of ICMP

1. Send echo requests from a TCP/IP device to another
   
   
2. Responds to Echo request
   
   
3. Helps to find routing path issues
   
   
4. ICMP echo message verify the availability of the destination

List of Messages Generated by ICMP

1. Address Request
   
   
2. Address reply
   
   
3. Destination unreachable
   
   To learn more about the Destination unreachable message generated by Internet Control Message Protocol, visit the links below.
   
   
   • Destination Net Unreachable
     
     
   • Destination Host Unreachable
     
   
   
4. Subnet Mask Request
   
   
5. Time Exceeded

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